Yes, I had the same experience as you and had to not just read but play around with the MDN docs example to get it. I still think the functional formatting is

Yes, I had the same experience as you and had to not just read but play around with the MDN docs example to get it. I still think the functional formatting is confusing. It makes sense, the pattern applies to every "A*n + B"th index (counting from the end) where n is every integer from 0..inf. But in my mind I'm just providing an offset and a step size/direction: (offset=B, step=A) or just (B A). I'd be interested to know why it's the way it is.